Acrylic rubber exhibits excellent oil resistance, heat resistance, and ozone resistance, and is therefore used in various hoses and seals, such as packings and gaskets.
Hoses and seals using acrylic rubber are produced by mixing acrylic rubber with a filler, an antioxidant, a processing aid, and a vulcanizing agent, molding by vulcanization, and then further carrying out secondary vulcanization. The vulcanizing steps complicate a process for producing a molding of acrylic rubber, and make it difficult to recycle a molding of acrylic rubber or a defective product generated during production of the molding.
In recent years, an olefinic thermoplastic elastomer has been widely used in place of vulcanized rubber in interior and exterior parts of automobiles and in the field of electric appliances.
For example, an olefinic thermoplastic elastomer comprising polypropylene and ethylene-propylene rubber (see Patent Document 1: Japanese Laid-Open Patent Publication No. 4826838 (pages 38 to 60)) and an olefinic thermoplastic elastomer comprising polypropylene and acrylonitrile-butadiene rubber (hereinafter abbreviated to NBR) (see Patent Document 2: Japanese Laid-Open Patent Publication No. 4-48817 (pages 5 to 12)) are known.
Since olefin resins and acrylic rubbers are inherently incompatible with each other, a favorable olefinic thermoplastic elastomer cannot be obtained if an olefin resin and acrylic rubber are simply blended. In this context, an olefinic thermoplastic elastomer produced by adding a compatibilizer that enhances compatibility between olefin resins and acrylic rubbers is known (see Patent Document 3: Japanese Laid-Open Patent Publication No. 60-156738 (pages 38 to 69)).
However, the olefinic thermoplastic elastomer disclosed in Patent Document 1 exhibits inferior oil resistance, and the olefinic thermoplastic elastomer disclosed in Patent Document 2 exhibits excellent oil resistance, but exhibits inferior heat resistance and weather resistance. Therefore, parts made of the elastomers of Patent Documents 1 and 2 are not suitable for use in places requiring both oil resistance and heat resistance, such as engine rooms in automobiles. Since olefin resins and acrylic rubbers are not sufficiently compatible in the olefinic thermoplastic elastomer of Patent Document 3, parts made of the elastomer still do not have sufficient oil resistance.
As described above, the olefinic thermoplastic elastomers of the prior art do not satisfy requirements for oil resistance, heat resistance, mechanical properties (which refer to compression set, tensile strength, elongation at break (or fracture elongation), and hardness in this specification), moldability, and recycling characteristics.